import pandas as pd
import statsmodels.api as sm
import streamlit as st
from datetime import datetime
import os

# ---- App title ----
st.title("Mini Stata - Simplified Version")

# ---- Student login ----
st.subheader("Student Login")
student_name = st.text_input("Enter your name:")
student_id = st.text_input("Enter your student ID:")

if student_name and student_id:
    logfile = f"log_{student_id}.csv"

    # Ensure log file exists
    if not os.path.exists(logfile):
        pd.DataFrame(columns=["timestamp", "student_name", "student_id", "command", "result"]).to_csv(logfile, index=False)

    st.success(f"Logged in as {student_name} (ID: {student_id})")

    # ---- File upload ----
    uploaded_file = st.file_uploader("Upload CSV file", type=["csv"])
    if uploaded_file is not None:
        df = pd.read_csv(uploaded_file)
        st.success("File uploaded successfully!")
    else:
        st.info("No file uploaded. Using default sample dataset.")
        df = pd.DataFrame({
            "mpg": [21, 22, 18, 30],
            "weight": [2500, 2800, 3200, 2100],
            "cyl": [4, 4, 6, 4],
            "horsepower": [90, 95, 110, 80]
        })

    # ---- summarize ----
    def summarize(var=None):
        try:
            if var is None:
                return df.describe().T
            elif var in df.columns:
                return df[var].describe().to_frame().T
            else:
                return f"Variable '{var}' not found."
        except Exception as e:
            return f"Error in summarize: {e}"

    # ---- browse ----
    def browse(n=None):
        try:
            if n is None:
                return df
            return df.head(n)
        except Exception as e:
            return f"Error in browse: {e}"

    # ---- tab ----
    def tab(var):
        try:
            if var not in df.columns:
                return f"Variable '{var}' not found."
            return df[var].value_counts().to_frame("Frequency")
        except Exception as e:
            return f"Error in tab: {e}"

    # ---- reg (simplified like Stata) ----
    def reg(dep_var, indep_vars):
        try:
            if dep_var not in df.columns:
                return f"Dependent variable '{dep_var}' not found."
            for v in indep_vars:
                if v not in df.columns:
                    return f"Independent variable '{v}' not found."

            X = sm.add_constant(df[indep_vars])
            y = df[dep_var]
            model = sm.OLS(y, X).fit()

            # Create clean results table
            results_table = pd.DataFrame({
                'Variable': model.params.index,
                'Coef.': model.params.values.round(4),
                'Std. Err.': model.bse.values.round(4),
                't': model.tvalues.values.round(3),
                'P>|t|': model.pvalues.values.round(3)
            })

            # Display concise summary
            summary_stats = f"Number of obs = {int(model.nobs)}    R-squared = {model.rsquared:.3f}"
            return results_table, summary_stats
        except Exception as e:
            return f"Error in regression: {e}"

    # ---- Command parser ----
    def run_command(cmd):
        parts = cmd.strip().split()
        if not parts:
            return "No command entered."
        command = parts[0].lower()
        args = parts[1:]

        if command == "summarize":
            return summarize(args[0]) if args else summarize()
        elif command == "browse":
            return browse()
        elif command == "tab":
            if not args:
                return "Usage: tab varname"
            return tab(args[0])
        elif command == "reg":
            if len(args) < 2:
                return "Usage: reg depvar indepvar1 indepvar2 ..."
            return reg(args[0], args[1:])
        else:
            return f"Unknown command: '{command}'. Available commands: summarize, browse, tab, reg."

    # ---- Interface ----
    st.markdown("""
    ### Available commands
    - `summarize`
    - `summarize mpg`
    - `browse`
    - `tab cyl`
    - `reg mpg weight horsepower`
    """)

    cmd = st.text_input("Enter command:")

    if st.button("Run"):
        result = run_command(cmd)

        # Log
        log_entry = {
            "timestamp": datetime.now().isoformat(),
            "student_name": student_name,
            "student_id": student_id,
            "command": cmd,
            "result": str(result)[:500]
        }
        pd.DataFrame([log_entry]).to_csv(logfile, mode="a", header=False, index=False)

        # Display result
        if isinstance(result, tuple):  # regression output
            table, stats = result
            st.text(stats)
            st.table(table)
        elif isinstance(result, pd.DataFrame):
            st.dataframe(result)
        else:
            st.text(result)

    if st.button("Download My Log"):
        with open(logfile, "r") as f:
            st.download_button("Click to download", f, file_name=logfile, mime="text/csv")

else:
    st.warning("Please enter name and student ID to start.")